Search for Direct Top Squark Pair Production with Higgs bosons in the Final State in pp collisions at √s = 8 TeV.

Further information

This analysis is documented in CMS-PAS-SUS-13-021.

Abstract

This note presents a search for direct top squark pair production followed by decays to Higgs bosons using events with one or two electrons or muons and several jets, with at least 3 of them identified as originating from a b quark. The analysis is performed with 19.5 fb-1 of proton-proton collision data at √s = 8 TeV recorded with the CMS detector at the LHC. The results are interpreted in the context of a simplified model with pair production of a top squark t̃2 decaying to a top squark t̃1 via t̃2 → H t̃1, followed by t̃1 → tχ ̃0. The interpretation concentrates on the region of signal mass parameter space M(t̃1)-M(χ0) ~ M(t), which is not covered by existing searches. The analysis excludes at the 95% confidence level top squarks with masses M( t̃2) up to about 450 GeV for M( t̃1) up to about 250 GeV.

Figures and Tables

Figure Caption
T6tthh.png Figure 1 : Diagram for t̃2 pair production for the t̃2 → H t̃1, followed by t̃1 → tχ ̃0 decay mode.
table1.png Table 1 : Summary of the signal and sideband region definitions. The requirement MET > 50 GeV is applied to all regions.
table2.png Table 2 : Summary of the relative uncertainties (in %) on the total background predictions. All uncertainties are derived for the total background prediction and are treated as uncorrelated from each other.
table3.png Table 3 : Background predictions and data counts for the four signal regions. The separate background contributions are indicated with the statistical uncertainty only. The uncertainties on the total background predictions contain the statistical and systematic components.
mt_1l3b_scaled.png Figure 2a : Comparison of the MT distributions in data and MC simulation for events satisfying the 3b signal region requirements. The background scale factors are applied to the simulation, so the yields in the signal region correspond to the data-driven background prediction. The vertical dashed line indicates the corresponding signal region requirement. The distribution for the model t̃2 → H t̃1 where M(t̃2) = 450 GeV and M(t̃1) = 275 GeV is stacked on top of the backgrounds. The last bin contains the overflow.
mt_1l4b_scaled.png Figure 2b : Comparison of the MT distributions in data and MC simulation for events satisfying the >=4b signal region requirements. The background scale factors are applied to the simulation, so the yields in the signal region correspond to the data-driven background prediction. The vertical dashed line indicates the corresponding signal region requirement. The distribution for the model t̃2 → H t̃1 where M(t̃2) = 450 GeV and M(t̃1) = 275 GeV is stacked on top of the backgrounds. The last bin contains the overflow.
mbb_2l3b_scaled.png Figure 3a : Comparison of the M(b, b) distributions in data and MC simulation for events satisfying the 3b signal region requirements. The background scale factors are applied to the simulation, so the yields in the signal region correspond to the data-driven background prediction. The underflow bin contains events where no pairs satisfy the kinematic constraints; the last bin contains the overflow. For the cases of N(b, b)  2 the mass of the pair closest to 125 GeV is shown. The vertical dashed line indicates the corresponding signal region requirement. The distribution for the model t̃2 → H t̃1 where M(t̃2) = 450 GeV and M(t̃1) = 275 GeV is stacked on top of the backgrounds.
mbb_2l4b_scaled.png Figure 3b : Comparison of the M(b, b) distributions in data and MC simulation for events satisfying the >=4b signal region requirements. The background scale factors are applied to the simulation, so the yields in the signal region correspond to the data-driven background prediction. The underflow bin contains events where no pairs satisfy the kinematic constraints; the last bin contains the overflow. For the cases of N(b, b)  2 the mass of the pair closest to 125 GeV is shown. The vertical dashed line indicates the corresponding signal region requirement. The distribution for the model t̃2 → H t̃1 where M(t̃2) = 450 GeV and M(t̃1) = 275 GeV is stacked on top of the backgrounds.
table4.png Table 4 : The expected (exp) and observed (obs) cross section upper limits in pb at 95% confidence for two choices of top squark masses (M(t̃2),M(t̃1))=(350, 175) GeV and (M(t̃2),M(t̃1))=(450, 275) GeV. The results for the individual signal regions and the combination are indicated.
exclusion.png Figure 4 : Interpretation of the result of the search for the model of t̃2 pair production with t̃2 → H t̃1 with 100% branching fraction. The lighter top squark t̃1 is assumed to subsequently decay via t̃1 → tχ ̃0 with 100% branching fraction. The color scale indicates the observed cross section upper limit. The observed,  1 standard deviation observed, median expected and  1 standard deviation expected exclusion contours are also indicated. The cross section limits are available in electronic format here: root file.

Additional material

Figure Caption
eff_1l3b.png Figure 5a : Acceptance times efficiency for signal events to satisfy the requirements of the signal region with 1 lepton and exactly 3 b jets. (Note the impact of a possible signal contribution in the sideband region is not accounted for in these efficiencies.) The version in electronic format can be found here: root file.
eff_1l4b.png Figure 5b : Acceptance times efficiency for signal events to satisfy the requirements of the signal region with 1 lepton and at least 4 b jets. (Note the impact of a possible signal contribution in the sideband region is not accounted for in these efficiencies.) The version in electronic format can be found here: root file.
eff_2l3b.png Figure 5c : Acceptance times efficiency for signal events to satisfy the requirements of the signal region with 2 leptons and exactly 3 b jets. (Note the impact of a possible signal contribution in the sideband region is not accounted for in these efficiencies.) The version in electronic format can be found here: root file.
eff_2l4b.png Figure 5d : Acceptance times efficiency for signal events to satisfy the requirements of the signal region with 2 leptons and at least 4 b jets. (Note the impact of a possible signal contribution in the sideband region is not accounted for in these efficiencies.) The version in electronic format can be found here: root file.

exclusion_1l3b.png Figure 6a : Cross section upper limit for signal events to satisfy the requirements of the signal region with 1 lepton and exactly 3 b jets.
exclusion_1l4b.png Figure 6b : Cross section upper limit for signal events to satisfy the requirements of the signal region with 1 lepton and at least 4 b jets.
exclusion_2l3b.png Figure 6c : Cross section upper limit for signal events to satisfy the requirements of the signal region with 2 leptons and exactly 3 b jets.
eff_2l4b.png Figure 6d : Cross section upper limit for signal events to satisfy the requirements of the signal region with 2 leptons and at least 4 b jets.

-- MariarosariaDalfonso - 11 Nov 2013

Topic attachments
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Unknown file formatroot SUS-13-021_efficiencies.root r3 r2 r1 manage 5.4 K 2013-11-23 - 18:52 VerenaMartinez  
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PDFpdf T6tthh.pdf r1 manage 9.6 K 2013-11-11 - 18:43 MariarosariaDalfonso  
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